Detergent compositions manufactured in the form of compacted detergent powder are known in the art. U.S. Pat. No. 5,225,100, for example, describes a tablet of compacted powder comprising an anionic detergent compound which will adequately disperse in the wash water.
Although detergent compositions in the form of compacted granular tablets of various shapes have received much attention in the patent literature, the use of such tablets to provide a unit dose fabric softener which will soften or condition fabrics in the wash cycle without impairing detergency or otherwise compromise the cleaning benefits provided by the detergent composition is not known.
Another possible option for providing a unit dose softener apart from the wash cycle is to introduce the softening ingredients directly into the rinse cycle. But, for this type of product to be effective several practical requirements must be met. To begin with, the size and shape of the unit dose container must be readily compatible with the geometry of a wide variety of rinse cycle dispensers designed for home washing machines in order to insure its easy introduction into the dispenser. Moreover, in common with the general use of rinse cycle softeners, it is necessary to clean the rinse dispenser on a regular basis to avoid residue from accumulating within the dispenser or even, at times, prevent bacterial growth from occurring.
Still further, a unit dose composition for the rinse cycle must be formulated to readily dispense its contents upon contact with water in a period of time corresponding to the residence time of the unit dose in the dispenser, namely, the period of time during which water enters and flows through the rinse cycle dispenser. The aforementioned practical requirements have to date not been successfully met with any commercially available product and hence there remains a need in the art for a unit dose softener capable of activation in the rinse cycle.
Laundry detergent compositions which further include a fabric softener to provide softening or conditioning of fabrics in the wash cycle of the laundering operation are well-known in the art and described in the patent literature. See, for example, U.S. Pat. No. 4,605,506 to Wixon; U.S. Pat. No. 4,818,421 to Boris et al. and U.S. Pat. No. 4,569,773 to Ramachandran et al., all assigned to Colgate-Palmolive Co., and U.S. Pat. No. 4,851,138 assigned to Aikzo. U.S. Pat. No. 5,972,870 to Anderson describes a multi-layered laundry tablet for washing which may include a detergent in the outer layer and a fabric softener, or water softener or fragrance in the inner layer. But, these type of multi-benefit products suffer from a common drawback, namely, there is an inherent compromise which the user necessarily makes between the cleaning and softening benefits provided by such products as compared to using a separate detergent composition solely for cleaning in the wash cycle and a separate softening composition solely for softening in the rinse cycle. In essence, the user of such detergent softener compositions does not have the ability to independently adjust the amount of detergent and softener added to the wash cycle of a machine in response to the cleaning and softening requirements of the particular wash load.
Some attempts have been made in the art to develop wash cycle active fabric softeners, typically in powder form. But, these type products are characterized by the same inconvenience inherent with the use of powered detergents, namely, problems of handling, caking in the container or wash cycle dispenser, and the need for a dosing device to deliver the desired amount of active softener material to the wash water.
The use of a unit dose wash cycle fabric softening composition in the form of a compacted granular tablet offers numerous advantages, but it is important that such tablets be sufficiently hard and not friable so as to withstand handling and transportation without breaking or fragmenting. In order to achieve the desired level of hardness, tablet makers generally tend to increase the compacting pressure. But, a high compacting pressure, if favorable to the hardness of the tablet, lowers the disintegration rate of such tablet.
To be effective, the unit dose fabric softening compositions, which are compacted granular compositions, must be able to disperse in the wash liquor in a short period of time to avoid any residue at the end of the wash cycle.
Typically, the wash cycle time can be as short as 12 minutes and as long as 90 minutes (in typical European washers) depending on the type of washer and the wash conditions. Therefore, to make sure that the compacted unit dose is properly dispersed in the wash liquor before the end of the cycle, disintegrating materials must be added to the granules before compacting. This need for disintegrating agents is well-known in the art and the most popular materials used for this purpose are water swelling polymers such as polyvinylpyrrolidone, cellulosic polymers or a blend of citric acid and bicarbonate salt that provide an effervescent matrix.
The problem with these disintegrating materials and swelling polymers is that they constitute a significant weight and cost of the overall composition and they serve only he single purpose of dispersion of the tablet. Also the use of a typical effervescent matrix results in a typical feel of the tablet surface that can be described as dry and "stony", which is generally not favored by consumers.
It has now been found that a particular grade of clay (described in WO 00/03959) can replace the usual disintegrating agents while contributing to the softness of the clothes. The use of such clay enhances the disintegration rate of the unit dose while allowing the use of higher compacting pressure and reducing the friability of the dose. Moreover, it provides the finished tablet with a very smooth feel.